A: You have to be careful when performing crunches on Swiss balls because they work the rectus abdominus through an extreme range of motion that does not normally occur in daily activities. As such, it is extremely easy to injure the abdominals with them; that’s the reason you have to start these exercises with no resistance.
If there is a need for special abdominal work, I prefer reverse situps because they minimally involve the hip flexors for assistance. Position yourself on a situp board facing away from the rollers, and grasp the handle. Keep your arms slightly bent to minimize the stress on your shoulders. Bend your knees so that your upper thighs are perpendicular to the floor; your feet should be off the floor and should not touch the floor throughout the exercise. Now lift your hips up and toward you as far as you can comfortably, and then return to the starting position.
To increase the difficulty, perform the exercise on an incline or from a hanging position. For this variation, an exercise often called the Garhammer raise, start with your thighs parallel to the floor, and then pull your knees to your chest. You can also hook a low pulley cable to an ankle attachment, which gives you a precise increase in resistance.